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Hiya Nick, Depend's on how deep a scratch is but I very much doubt it as even though I may be taking a lot of glass off (in polishing terms) it's a small amount. Fingers crossed though as mine are very light. I have another couple of hours planned this aft so I shall take some image's later on of the progress Damian

Hiya Ron I know It sounds extreme but that's what John and also Raymond now have advised me to do. I did it quite a few time's on the larger lap to no detriment but I must admit I'm always a bit apprehensive once I've done it. I do have a couple of small scratches on the mirror which will have to stay at this point but not caused by the brushing. One will probably be under the shadow of the secondary. Damian

Hi Alan I'm glad to hear you've read the whole thread and found it interesting, if only to appreciate the incredible experience and dedication that mirror makers such as John have to create such master pieces. As an amateur I'm inexperienced and obviously feeling my way along so to say if very slowly. There is lots of input from mirror makers experienced and other wise from right around the globe here which is good and it does create quite a discussion sometimes. As with scope's there isn't one that is the same or made exactly the same, although if they were we'd all be looking through Kriege and Berry style dobs and you wouldn't have the Canopus agreed? I hope to read your first light report Alan as it's a beautiful scope and the one that inspired me to build something a little different and will do in the future. Thanks again for reading Damian P.s. I'm not saying which christmas but I think I'll get lynched if it's not done for november

I have been doing the wire brush scrub but not quite often enough by the sound's of it. Great tip and thanks for that Raymond. I will test the mirror later after a cool down and see if things have changed for the better. Can I also add that is one lovely Flickr page you have Damian

There's no rush but I thought I'd try a different tactic. As you say Nigel I will keep a close eye on the centre as I proceed and if it is going wrong I will revert to the edge. As RAC says it is a large fast mirror and the amount of glass to remove is a lot so I am trying to kill two birds with one stone by working both for now if things start to go awry I can change back. The lap has a lot of micro faceting on it, I am probably wrong but it seems to be working o.k. Damian

The pressing depends on the temperature and weight you put on. If it's warmed up too much it will just close the gaps up very quickly as will sticking lots of weight on. Smaller lap less weight (5 to 10kg). I normally soak it in luke warm water for 5-10mins so the lap is warmed through and then a half hour press. The lap is left on grease proof paper ontop of the mirror when I'm not working on it so it retains it's shape. Which reminds me it's been pressing for a good hour now

With work and chores over with yesterday and today it's back to the mirror campaign. To start with the lap facet's were looking closed up, so out with the saw and half an hour later the lap channels were cut and I was ready for a bit of warming and pressing. Not the prettiest or neatest lap in the world but it's worked up to now. This is the third time I've re-cut the facet's and it happens quite often. Today I'm going to start the parabolising process as this may bring the edge to heel. On with the W strokes Damian

Thanks Ron There's no rush as I've got this far and will get to the end. Great that you guys keep following my slow progress and offer encouragement John offers great advice and encouragement in the back ground which I've not mentioned much It's always nice to see the other opinions on what you guys think too. I may get a few strokes done today but I need to catch up on a few chores first as my cleaner has been busy fighting a turned down edge Damian ;-)

Ha ha yeah Maybe a bit more work today but I need to concentrate on other bit's today

I think there were a few others trying to corrupt me in Galloway!

Hiya Derek Everything is a good idea so no shooting will occur. I was disheartened a couple of week's ago, but spirits are quite high at present and yes things don't work out sometimes and that's where more advice and effort are required. I knew it was going to be hard from the start as John had said but it is doable. I've been thinking it may be technique but it could also be other issues that have been at the back of my thought's Raymond has made a good suggestion which confirms what John had said about large fast mirrors so after a few other bit's tomorrow I will continue. I also know your not nuts as you've not started mirror making yet ;-)

I have done about another 2 hours during the day, I think I may have a beer now as I think I deserve one

Saying it's not changed much I have a nice little hill forming in the middle just to explain why the line's aren't straight in the central area. This tallies with being opposite to the lines at the edge inside and outside ROC

I have been told this already Raymond as larger mirror's respond differently to the smaller stuff, I have tried again today to remove the offending edge using chordal strokes with the centre of the lap 2" from the edge, it has changed very little Inside ROC Outside ROC So with a view to possibly sort the edge I will have a re-read of some info then go with the W strokes. Thanks for the comments guy's Damian

No problem Derek I think it's love and hate to be actually honest ha ha

Hi Derek. What I'm looking for is the lines inside and outside the radius of curvature to be completely vertical. When the edge is turned down (as mine is) it shows as the lines bending inwards near the edge when the image is taken inside radius of curvature (ROC) and outwards outside the ROC as mine do. Here's how a perfect sphere should look inside and outside ROC And here's a TDE outside ROC As you can see it's just the very edge that's the problem at present. Once I'm to a sphere I can move on to the parabolising process although for a large mirror like this everything takes an age to alter. Judging change is very difficult so you have to stick with your chosen tactic for a while to see the difference be it right or wrong and that's why it's a back and forth testing game Hope that explains Damian

I'm now working with a 10" lap John and have been for the last few page's on the thread. More work today and concentrating more on edge work than the centre. Looking like a lovely spiral galaxy These things take time and it get's very difficult to see any movement on the image's Inside ROC Outside ROC More work to follow and I'll post an update later Damian

I managed an hour yesterday working exclusively on the edge. Not much change but I have all today planned on it so again I will concentrate on the edge and leave the middle to deal with later. Will update this evening Damian

Great stuff Rich I look forward to the progress report

Thank you for that Raymond. Nice to know that the Ronchi test was the main tool you used in the making of your superb mirror as some don't really like it. In my opinion it's easy to set up, use and is not over complicated like some of the other test method's mentioned which is all good for someone that is an amateur. If it produces a mirror that is close for me then the last stages will be a null test and finally an auto collimation test by experienced eye's. Back to technique, as I work the mirror it is rotated randomly between wet's to avoid astigmatism and hopefully produce a figure of rotation Explaining your test methods and how you had to rework your mirror to end up with the finished item is a help as it proves it can be done several way's. Much respect for finishing a lovely looking mirror Damian

Hi RickI normally leave the mirror after washing it off under cold water for a couple of hours but then retest just before another session so it will be tomorrow morning when I have another look. As you say the edge is getting nearer but it's so hard to judge changes Damian

I've just been busy with the camera again before I get ready for work Here's the result's of this morning's efforts Inside ROC Outside ROC I have used the same W type stroke as before deepening all the curve but the last half an hour I just worked across the middle 1/3 of the mirror with approx 1/2" overhang in a attempt to push the TDE out. It's also flattened the hill a little More thinking this aft before returning to the fray tomorrow morning with renewed vigour Damian

Great info Ron. I have read about the way the facets work before but cannot remember there is a full page on the web about it somewhere? Tex also has a bit in his book about the surface quality using various type's of lap although the picture's are quite dated now it does give a good representation of what it looks like at a microscopic level. I have done another 2 hour's today so the mirror is just settling before I put it to the test again, I like the bit about giving it a quiet talking to although I must admit it's not responding well to the expletive's that I sometime's use I shall post some image's although I do believe they may not be much different to the one's above in the TDE battle Damian

Hello John, A lot of thought's there thanks and just to elaborate on a few bit's which I have touched on in previous post's which maybe you missed??? I'd be surprised myself if I made a full size lap as I would probably need me to spend quite a bit of time in the gym to push it across the surface, the amount of drag on an 18" lap is phenomenal and I have 40kg of weight on the base of the table and the suction still tried to lift the legs. It's hard work I will give thought to the test you mention as the diffraction around the Ronchi image's is quite severe so other method's may be needed although the Ronchi does show a lot. Several people have already commented on lap making via the 'Tex' cutting squares method and it is something I will considered if I make another lap. I'll probably have a go at it as I have tried several other way's (in previous post's) although everything is good in theory and I suspect it will end up a very messy affair I'll definitely agree with you on a few of your point's . The pitch bit, that it stick's to everything mostly what you don't want it to hot or cold! That you have never made anything as big as this by suggesting working mirror on top or making a full size lap both of which just aren't practical or feasible due to the physical effort needed to use them The creation of micro facets is a good idea, either by the onion bag method or by placing the wet lap on greaseproof paper whilst pressing which wrinkles the paper and after several uses create's micro faceting Damian

That look's very nice Raymond and a pleasure to behold, certainly inspirational On a testing point did you use a matched Ronchi test for it to start with? and obviously other test's? Could you explain your testing as it's obviously produced a very nice mirror as can be seen from your image. I one day hope to be in the same position of being able to say been there done that and I have the picture's and test image's to prove it. Well done and thank you for sharing it with us, can we also see a pic when you get it coated. Damian